THYROID SCREENING AND RELIABILITY OF RADIATION THYROID DOSES FOR THE BELARUSIAN IN UTERO COHORT.

OBJECTIVE: To describe the status and results of thyroid disease screening and assessment of reliability of radiationthyroid doses in the Belarusian in utero cohort of 2,965 individuals exposed to Chernobyl (Chornobyl) fallout. MATERIALS AND METHODS: Thyroid screening examinations are currently underway including thyroid palpation by anendocrinologist, ultrasonographic examination by an ultrasonographer and analysis of blood samples for diagnosisof hypo- and hyperthyroidism, autoimmune thyroiditis, thyroid function tests (thyroid-stimulating hormone [TSH],thyroxine [T4], thyroid peroxidase antibody [anti-TPO], and thyroglobulin antibodies [anti-TG]). Reliability of (i)information from 780 pairs of questionnaires obtained during the first and second interviews of the mothers and (ii)thyroid doses, which were calculated for the cohort members using this information, is evaluated. RESULTS: As of 15 August 2021, 1,267 in utero exposed study subjects had been screened. A single thyroid nodule wasdiagnosed in 167 persons (13.2 % of the total) and multiple thyroid nodules in 101 persons (8.0 %): 189 (14.9 %)persons had nodules detected for the first time at the screening while 79 (6.2 %) persons had nodules detected pre-viously (pre-screening nodules). Fifty-nine out of 268 subjects (22.0 %) with a suspicious thyroid nodule werereferred to fine needle aspiration biopsy, and among them 33 (55.9 %) were biopsied. Reasonable agreement wasobserved for modelqbased doses calculated for the Belarusian in utero cohort members using data from the two inter-views (Spearman's rank-correlation coefficient rs = 0.74, p < 0.001), while measurementqbased doses yielded almost per-fect agreement (rs = 0.99, p < 0.001). CONCLUSIONS: During the thyroid screening, at least one thyroid nodule was identified in 268 of 1,267 (21.2 %) inutero exposed cohort members. Seven thyroid cancer cases were identified in the cohort, including 5 pre-screeningcases and 2 cases detected during the screening. Ongoing research on this unique cohort will provide importantinformation on adverse health effects following prenatal and postnatal exposure to radioiodine and radiocesium iso-topes, for which available epidemiological data are scant.

Thyroid cancer risk in Belarus among children and adolescents exposed to radioiodine after the Chornobyl accident.

BACKGROUND: Previous studies showed an increased risk of thyroid cancer among children and adolescents exposed to radioactive iodines released after the Chornobyl (Chernobyl) accident, but the effects of screening, iodine deficiency, age at exposure and other factors on the dose-response are poorly understood. METHODS: We screened 11 970 individuals in Belarus aged 18 years or younger at the time of the accident who had estimated (131)I thyroid doses based on individual thyroid activity measurements and dosimetric data from questionnaires. The excess odds ratio per gray (EOR/Gy) was modelled using linear and linear-exponential functions. RESULTS: For thyroid doses <5 Gy, the dose-response was linear (n=85; EOR/Gy=2.15, 95% confidence interval: 0.81-5.47), but at higher doses the excess risk fell. The EOR/Gy was significantly increased among those with prior or screening-detected diffuse goiter, and larger for men than women, and for persons exposed before age 5 than those exposed between 5 and 18 years, although not statistically significant. A somewhat higher EOR/Gy was estimated for validated pre-screening cases. CONCLUSION: 10-15 years after the Chornobyl accident, thyroid cancer risk was significantly increased among individuals exposed to fallout as children or adolescents, but the risk appeared to be lower than in other Chornobyl studies and studies of childhood external irradiation.

Monte Carlo modeling of beta-radiometer device used to measure milk contaminated as a result of the Chernobyl accident.

This paper presents results of Monte Carlo modeling of the beta-radiometer device with Geiger-Mueller detector used in Belarus and Russia to measure the radioactive contamination of milk after the Chernobyl accident. This type of detector, which is not energy selective, measured the total beta-activity of the radionuclide mix. A mathematical model of the beta-radiometer device, namely DP-100, was developed, and the calibration factors for the different radionuclides that might contribute to the milk contamination were calculated. The estimated calibration factors for (131)I, (137)Cs, (134)Cs, (90)Sr, (144)Ce, and (106)Ru reasonably agree with calibration factors determined experimentally. The calculated calibration factors for (132)Te, (132)I, (133)I, (136)Cs, (89)Sr, (103)Ru, (140)Ba, (140)La, and (141)Ce had not been previously determined experimentally. The obtained results allow to derive the activity of specific radionuclides, in particular (131)I, from the results of the total beta-activity measurements in milk. Results of this study are important for the purposes of retrospective dosimetry that uses measurements of radioactivity in environmental samples performed with beta-radiometer devices.

Measurement of 129 I and 137 Cs in soils from Belarus and reconstruction of 131I deposition from the Chernobyl accident.

I and Cs have been measured in a large number of soil samples collected throughout the country of Belarus to support efforts for thyroid-dose reconstruction following the Chernobyl accident. Samples of soil consisting of multiple 30-cm-deep cores per site were sampled following a selection process to ensure sites were undisturbed and representative. Samples were measured by accelerator mass spectrometry (AMS) for I, gamma spectrometry for Cs, and gas chromatography (GC) for total iodine. Results show that both I and Cs are retained firmly in the top approximately 15 to 20 cm of the soil. Our results also suggest that the correlation between I and Cs deposition across the country of Belarus is poor; hence, I is a better surrogate for I than is Cs. It was also noted that total iodine concentrations in topsoil from Belarus are low compared with other regions of the world where radiogenic thyroid cancer has been studied.

Uncertainties in thyroid dose reconstruction after Chernobyl.

The most significant impact of the Chernobyl accident of 26 April 1986 is the increased incidence of thyroid cancer among Belarusians, Russians and Ukrainians who were exposed as children to radioiodines in fallout resulting from atmospheric releases. The US National Cancer Institute (NCI), in cooperation with the ministries of health of Belarus and Ukraine, is involved in epidemiological studies of thyroid diseases related to the accident. Individual thyroid doses, as well as uncertainties, have been estimated for the members of the cohort studies (approximately 13,000 Ukrainians and 12,000 Belarusians). The cohort subjects, who were selected from the large group of children whose thyroids were monitored for gamma radiation within a few weeks of the accident, provided personal information on their residence history and dietary habits during interviews. Thyroid dose estimates range from 1 mGy to more than 20 Gy. The uncertainties are found to be approximately log-normally distributed, with geometric standard deviations ranging from 1.6 to 5.0. The medians of the geometric standard deviations are 1.7 for the Ukrainian subjects and 2.1 for the Belarusian subjects. The major sources of uncertainty in the thyroid dose estimates are found to be those related to the thyroid mass of the subject and to the estimation of the thyroidal content of 131I at the time of thyroid monitoring.

Chernobyl-related thyroid cancer in children of Belarus: a case-control study.

The accident at the Chernobyl nuclear power plant on April 26, 1986, released approximately 2 EBq of 131I and other radioiodine isotopes that heavily contaminated southern Belarus. An increase in thyroid cancer reported in 1992 and attributed to the Chernobyl accident was challenged as possibly the result of intensive screening. We began a case-control study to test the hypothesis that the Chernobyl accident caused the increase in thyroid cancer. Records of childhood thyroid cancer in the national therapy centers in Minsk in 1992 yielded 107 individuals with confirmed pathology diagnoses and available for interview. Pathways to diagnosis were (1) routine endocrinological screening in 63, (2) presentation with enlarged or nodular thyroid in 25 and (3) an incidental finding in 19. Two sets of controls were chosen, one matched on pathway to diagnosis, the other representing the area of heavy fallout, both matched on age, sex and rural/urban residence in 1986. The 131I dose to the thyroid was estimated from ground deposition of 137Cs, ground deposition of 131I, a data bank of 1986 thyroid radiation measurements, questionnaires and interviews. Highly significant differences were observed between cases and controls (both sets) with respect to dose. The differences persisted within pathway to diagnosis, gender, age and year of diagnosis, and level of iodine in the soil, and were most marked in the southern portion of the Gomel region. The case-control comparisons indicate a strong relationship between thyroid cancer and estimated radiation dose from the Chernobyl accident.

Thyroid dose reconstruction for the population of Belarus after the Chernobyl accident.

An 131I environment transfer model--adapted for Belorussian conditions--was applied to estimate thyroid doses for different population groups. For this purpose the available data were analysed and the important radioecological parameters assessed i.e. (a) the elimination rate of 131I from grass due to weathering and growth dilution, (b) the initial interception of 131I by vegetation, (c) the transfer coefficient for 131I from grass to cow's milk, (d) the yield to pasture grass and (e) the milk consumption rate. Additionally, the influence of applied countermeasures has been taken into account, such as the interruption of locally produced milk consumption, and the appropriate correction factors have been estimated. As a result, the average age-dependent thyroid doses were assessed for the Belorussian population. The highest average doses in children (> 1 Gy) have been estimated for the Bragin, Khoiniki, Narovlia and Vetka raions of the Gomel oblast. The thyroid exposure tends to decrease from the southeastern (closest to the Chernobyl nuclear power plant areas) to the northwestern part of the republic. When comparing the assessed thyroid doses with estimates derived from direct 131I activity measurements in thyroids (for the locations with more than 15 direct measurements), the results agree fairly well. The model calculation may perhaps overestimate thyroid doses of the population residing in the settlements of the central and northern parts of Belarus, distant from the areas with direct measurements of 131I activities in soil, grass and milk. These thyroid dose estimates may serve as a basis for further epidemiological studies and risk analyses.

Influence of measurement geometry on the estimate of 131(I) activity in the thyroid: Monte Carlo simulation of a detector and a phantom.

An approach for evaluating the influence of measurement geometry on estimates of 131(I) in the thyroid from measurements with survey meters was developed using Monte Carlo simulation of radiation transport in the human body and the radiation detector. The modified Monte Carlo code, EGS4, including a newly developed mathematical model of detector, thyroid gland, and neck, was used for the computations. The approach was tested by comparing calculated and measured differential and integral detector characteristics. This procedure was applied to estimate uncertainties in direct thyroid-measurement results due to geometrical errors.

Emerging technological bases for retrospective dosimetry.

In this article we discuss examples of challenging problems in retrospective dosimetry and describe some promising solutions. The ability to make measurements by accelerator mass spectrometry and luminescence techniques promises to provide improved dosimetry for regions of Belarus, Ukraine and Russian Federation contaminated by radionuclides from the Chernobyl accident. In addition, it may soon be possible to resolve the large neutron discrepancy in the dosimetry system for Hiroshima through novel measurement techniques that can be used to reconstruct the fast-neutron fluence emitted by the bomb some 51 years ago. Important advances in molecular cytogenetics and electron paramagnetic resonance measurements have produced biodosimeters that show potential in retrospective dosimetry. The most promising of these are the frequency of reciprocal translocations measured in chromosomes of blood lymphocytes using fluorescence in situ hybridization and the electron paramagnetic resonance signal in tooth enamel.

The feasibility of using 129I to reconstruct 131I deposition from the Chernobyl reactor accident.

Radioiodine released to the atmosphere from the accident at the Chernobyl nuclear power station in the spring of 1986 resulted in large-scale thyroid-gland exposure of populations in Ukraine, Belarus, and Russia. Because of the short half life of 131I (8.04 d), adequate data on the intensities and patterns of iodine deposition were not collected, especially in the regions where the incidence of childhood-thyroid cancer is now increasing. Results are presented from a feasibility study that show that accelerator-mass-spectrometry measurements of 129I (half life 16 x 106 y) in soil can be used to reconstruct 131I-deposition density and thus help in the thyroid-dosimetry effort that is now urgently needed to support epidemiologic studies of childhood-thyroid cancer in the affected regions.

The first international intercomparison of EPR-dosimetry with teeth: first results.

Intercomparison of EPR-dosimetric techniques using tooth enamel had been performed in order to check whether the results produced by different laboratories are consistent and accurate. Participants were supposed to evaluate doses applied to pulverized enamel samples, using routine techniques from their laboratories. The intercomparison has demonstrated a great variety of methods used for dose reconstruction. Peculiarities of experimental approaches are discussed systematically in terms of procedure for recording the EPR-spectra, determination of the amplitude of the radiation induced signal, determination of the dose, and error propagation.

Radiation effects on the population of Belarus after the Chernobyl accident and the prediction of stochastic effects.

Evaluation of conditions of exposure during the post-accident period makes it possible to identify two periods in the radiation exposure of Belarus's population. As a result of our investigations we obtained data about doses for four different categories in the exposed population: people who lived in the contaminated territories without evacuation and relocation; evacuated people: cleanup workers ("liquidators"); and people who were exposed in childhood, especially for thyroid exposure. The total doses for these categories in different time periods were analysed. Evaluation of doses received by the Belarusian population due to the Chernobyl accident shows no evidence of doses, that could lead to the deterministic consequences of radiation exposure. For all exposed groups we made predictions about different types of stochastic consequences of exposure.

[Soft- and hardware support for the setup for computer tracking of radiation teletherapy]. / Programmnoe i apparaturnoe obespechenie kompleksa soprovozhdeniia distantsionnoi luchevoi terapii s pomoshch'iu EVM.

A hard and soft ware computer assisted complex has been worked out for gamma-beam therapy. The complex included all radiotherapeutic units, including a Siemens program controlled betatron with an energy of 42 MEV computer ES-1022, a Medigraf system of the processing of graphic information, a Mars-256 system for control over the homogeneity of distribution of dose rate on the field of irradiation and a package of mathematical programs to select a plan of irradiation of various tumor sites. The prospects of the utilization of such complexes in the dosimetric support of radiation therapy are discussed.

[Evaluation of radiation treatment effectiveness using the rated standard dose (RSD) under different irradiation conditions]. / Otsenka éffektivnosti luchevogo lecheniia s pomoshch'iu NSD pri razlichnykh usloviiakh oblucheniia.

In the evaluation of efficacy or while comparing various irradiation schemes with the help of the RSD concept one should consider the effect of various conditions of patient's irradiation (energy, a field size, dose rate, etc.) on the biological efficacy of absorbed energy. The radiobiological effect of various irradiation schemes should be evaluated by a common scale, therefore factors altering dose biological efficacy should be considered within the limits of the same RSD formula. In our opinion, there is no sense in individualizing the evaluation of an effect of the dose rate on the biological efficacy of radiotherapy as a separate RSD formula. The incorporation in the RSD formula of an empirical expression of RBE dependence on the dose rate within the range of 0.13-300 Gy/hr. and factors of the dependence of dose biological efficacy on its spatial distribution (energy, a field size) gives an opportunity not only to consider more correctly changes in patient's irradiation from session to session but also makes it possible to apply it to fractionated and protracted irradiation schemes.

[Computerized program for calculating the dose distribution generated by intracavitary linear sources of gamma radiation]. / Programma rascheta na EVM doznogo raspredeleniia, sozdavaemogo vnutripolostnymi lineimymi istochnikami gamma-izlucheniia.

One can achieve a high precision in the dosing of a session of intracavitary radiotherapy by rapid computerization of the treatment time that is necessary for obtaining a certain dose in a pathological focus taking account of an actual location of radiation sources in the process of irradiation. The authors have developed an algorithm and drawn up a program for computer ES-1022 to calculate a dose rate in any point of an irradiated volume from the system of gamma-radiation sources oriented arbitrarily in space. As part of a hard- and soft ware dosimetric complex, the above program provides for the calculation of the treatment time by a set dose; the time is necessary for supplying this dose to a tumor focus taking account of an actual location of radiation sources during a session of irradiation. The whole computer procedure from the moment of obtaining necessary anatomo-topographic information in the form of two x-ray pictures up to the output of an irradiation session time value and other information into the alpha-numeric printer takes 3-5 min. The program makes it possible to calculate dose distribution in any preset plane (up to 4 planes at a time) of an irradiated volume.